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DAM SYNCHRONISATION AND FLOOD RELEASES IN THE ZAMBEZI RIVER BASIN: ANNEX 4 OF FINAL REPORT 2.5 Evaluation of the criteria of this study A B C D E F G H Criterion Technical and legal feasibility Contribution to flood protection Impact on Ecosystems Cost effectiveness Impact on human use Biophysical impact Likelihood of realization Impact on more than one country Figure 2.3: Assessment of Shire flow regulation options (see Fig. 1.2 for legend) Upgrading Kamuzu Barrage Mponda Pumping Scheme Kholombidzo Reservoir High Kholombidzo Reservoir Low Technical and legal feasibility The Upgraded Kamuzu Barrage and the pumping barrage at Mponda have passed feasibility stage. The Kholombidzo Reservoir Low and High are also physically and legally feasible although there is still discussion about the socio-economic and environmental impacts. Contribution to flood protection The different impacts on flood protection are as follows: an upgraded Kamuzu Barrage will not help in flood control, other than removing the obstruction of the currently stuck flood gate and improving the conditions under which the operation of the dam can be done; a pumping scheme at Mponda will not contribute to flood protection, as it is meant for low water levels; and a new Kholombidzo Reservoir (high or low) could contribute to flood protection downstream, unless it is kept at its optimal level for hydropower production and little storage remains for flood attenuation. However, the reservoir itself would also flood some area. For a Kholombidzo high reservoir this area extends upto Kamuzu Barrage and may even influence Lake Malawi levels. For further explanation, reference is made to Annex 2 Concepts and Recommendations for Dam Management, Chapter 6. Other investment options It is clear that downstream tributaries have a large impact on flooding in the lower Shire, so new dams on these unregulated tributaries are likely to enhance flood control on the Lower Shire. 12
DAM SYNCHRONISATION AND FLOOD RELEASES IN THE ZAMBEZI RIVER BASIN: ANNEX 4 OF FINAL REPORT The alternative idea of a Tomaninjobi Stilling Basin for the Ruo Floods would need further investigation to be compared with the investment options presented here. Impact on ecosystems For evaluation of the impact on ecosystems, the upstream impact on Lake Malawi was decisive in the experts evaluation, as the downstream effects would depend on the operation of the investment rather than the realization of the investment, as described in Annex 2, Chapter 6. Lake Malawi was classified conservation priority 1 (globally outstanding and highly threatened) by dozens of specialists brought together in 2005 to classify the bioregions and freshwater ecoregions of Africa. Conservation priority 1 means that modifying such an eco-region is considered ‗unacceptable‘ by these specialists. From these three options: The upgrading of Kamuzu barrage is considered the least destructive and is scored ‗moderate to low impact‘; A pumping scheme at Mponda can result in more frequent low levels of Lake Malawi and is scored ‗high impact‘; and The Kholombidzo Reservoir High will not only lead to further flow regulation but also connect Lake Malawi with the reservoir. The Kholombizo dam is therefore ‗strongly not recommended‘. A lower dam, which should be lower than the current proposed Low Kholombidzo alternative, would have a score ‗high negative impact‘. Upgrading of Kamuzu Barrage Over the past century the Lake level changed by 7 m and fish (cichlids) have evolved with the changes in Lake levels. The effect of a higher maximum operating level of 0.2 m will translate into 0.14 cm higher lake levels, which mean that the chances of extra flooding of the Lake shores increase. Annex 2, Chapter 6, shows computations suggest that with an upgraded Barrage the critical level of 476.0 m will be exceeded 3% of the time. The Upgraded Liwonde Barrage will therefore not have any major impact on the long-term natural variation in lake levels. Rocky areas are quite prominent in the southern part of Lake Malawi which is most affected by the increased operating level, and these rocky areas provide breeding grounds for fish (Norconsult, 2003d). During the high water levels of the 1980s there has been reported wide spread breeding and abundance of fish. The EIA on the upgrading of Kamuzu Barrage currently being carried out will be more conclusive in this regard. Pumping scheme at Mponda With use of the Mponda pumps the highest levels of Lake Malawi will stay the same but the lowest levels will go down. The low levels may dry out vital habitats and exposed habitats that have not been exposed before. A larger ‗dead‘ zone around the lake will be created. Erosion may occur at the mouth of small perennial rivers entering the Lake. There is possibility of some streams being cut-off from the lake, when the Lake level is lower, but the Consultant expects that the rivers and streams flowing into the lake have enough gradient to deposit their run-off into the lake. This may further increase the drawdown of Lake Malawi. When in a cycle of dry years, impacts may extend over longer than usual periods. In the Norconsult report (2003d) it was mentioned that the negative impact on cichlid species was most pronounced. If Lake levels continue to be drawn down below 370 m.a.s.l., the ground water levels may drop in sympathy, with consequent negative environmental impacts. 13
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